The present disclosure relates to phase-sensitive calibration of a spatial light modulator (“SLM”) system. In particular, it relates to selecting among local calibrations when there is more than one calibration that satisfies a calibration intensity criteria. It utilizes information available before Fourier filtering, from non-zeroth order diffraction components to counter drift among alternative local calibrations.
Micro-lithographic production is useful for integrated circuits, masks, reticles, flat panel displays, micro-mechanical or micro-optical devices and packaging devices, e.g. lead frames and MCMs. Lithographic production may involve an optical system to image a master pattern onto a mask from an SLM controlled by a computer or to image the pattern directly onto a wafer, in both processes forming structures of a device. A suitable workpiece may include a layer sensitive to electromagnetic radiation, for example visible or non-visible light, applied to a quartz reticle or to a silicon wafer.
The computer-controlled SLM may include a one- or two-dimensional array or matrix of reflective movable micro mirrors, a one- or two-dimensional array or matrix of transmissive LCD crystals, or other similar programmable one- or two-dimensional arrays based on gratings effects, interference effects or mechanical elements (e.g., shutters).
In general, these computer controlled SLMs may be used for the formation of images in a variety of ways. SLMs include many modulating elements, in some instances, a million or more elements. Among the many modulating elements, individual elements most probably do not exhibit identical characteristics. For instance, they may have different reflectivity or they may respond differently to equivalent control signals. These variations in the characteristics of the individual elements of a computer controlled SLM have limited the resolution and accuracy available for their use in optical imaging.
An opportunity arises to improve calibration using information from multiple diffraction orders of a calibration pattern. Better, more easily calibrated and controlled, more reliable and accurate systems and methods of patterning workpieces and producing features on devices may result.